lac operon

1
lac operon
Repressor genes
Promoter
Operator
lac Z
lac Y
lac A
DNA
Repressor protein
Transcription
mRNA
Translation
Ribosome
(a)
2
lac operon
Repressor genes
Promoter
Operator
lac Z
lac Y
lac A
Transcription
mRNA
mRNA
Translation
Galactoside transacetylase
Galactose permease
Inducer (allolactose)
ß-galactosidase
Enzymes for lactose metabolism
Repressor protein (inactive)
(b)
3
lac operon
Repressor genes
Promoter
Operator
Trp E
Trp D
Trp C
Trp B
Trp A
DNA
RNA polymerase
Transcription
mRNA
mRNA
Translation
Enzymes of the tryptophan biosynthetic pathway
Repressor protein (inactive)
Tryptophan
4
trp operon
Repressor genes
Promoter
Operator
Trp E
Trp D
Trp C
Trp B
Trp A
DNA
Active repressor- corepressor complex
mRNA
Inactive repressor protein
Tryptophan (corepressor)
5
Promoter
RNA polymerase- binding site
CAP- binding site
Repressor genes
Operator
lac Z
lac Y
lac A
DNA
Transcription
RNA polymerase binds efficiently
mRNA
mRNA
CAP
Galactoside transacetylase
Translation
Galactose permease
cAMP
ß-galactosidase
Allolactose
Enzymes for lactose metabolism
Repressor protein (inactive)
(b)
6
Figure 13-8Page 266
COO-
Finger 2
Turn
Finger 3
Zinc ion
a-helix
Finger 1
Leucine zipper region
NH3
DNA
DNA
DNA
(a)
(b)
(c)
7
TATA box
Transcription initiation site (1)
T
T
TATA A
UPE
A
A
pre-mRNA
(a)
TATA box
Transcription initiation site (1)
UPE
pre-mRNA
(b)
8
Figure 13-7cPage 265
TATA box
Transcription initiation site (1)
UPE
UPE
UPE
UPE
pre-mRNA
(c)
9
Transcription initiation site (1)
UPE
UPE
pre-mRNA
(d)
10
Enhancer
Target proteins
RNA polymerase
TATA box
DNA
(a) Little or no transcription
Enhancer
Activator (transcription factor)
TATA box
DNA
(b) High rate of transcription
11
Figure 13-10Page 267
(a) Heterochromatin
Chromatin decondensation
Nucleosome
Histones
DNA
Transcribed region
(b) Euchromatin
12
Potential splice sites
Exon or intron
Exon
Intron
Exon
5
3
Differential mRNA processing
Exon
Exon
Exon
Exon
Exon
5
3
5
3
Functional mRNA in Tissue A
Functional mRNA in Tissue B